Process for testing driving axles and device for performing the process

ABSTRACT

A method of and apparatus for testing axles for motor vehicles and especially the drive axles for trucks, has a testing stand in which the axles are supported and connected to a drive motor and load. In addition to the driving forces which can thus be applied to the axle shaft, the axle housing can be loaded to represent truck loading and can be subjected to torsional stresses like those which are generated when the truck is inclined in driving. The shaft ends are laterally loaded as well to represent reaction forces from the wheel disks. The method and apparatus enable total testing of the functions of the axle under simultaneous drive and carrying conditions in a single operation on the stand.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase application corresponding toPCT/DE87/00586 which is based, in turn, on German National Application P36 42 2717.9 filed 13 December 1986 under the International Convention.

FIELD OF THE INVENTION

My present invention relates to a process for testing driving axleswherein the driving axle is mounted in a test stand driven from thedriving side and braked from the driven side.

Further, the invention relates to a device for testing driving axles formotor vehicles, consisting of a driving unit, which is generally linkedto the axle transmission by an axle drive shaft and composed of an axlehousing with linking elements between the axle shafts and a braking unitopposing resistance to rotation.

The term "driving axle" as used here encompasses the entire unitconsisting of axle housing, axle transmission, and one or severaldriving axles, whereby the axle transmission is driven by an externaldriven shaft, shifting the thereby produced torque and transmitting itto the axle shaft, which in turn is linked on a driven side with theso-called "driving wheel", which in a test stand is replaced by theso-called "wheel mounting". The ideal image formed by mathematicallines, whereupon the axle shafts revolve and which occasionally are alsocalled "axes", are subsequently called "rotation axes" in order to bebetter distinguished from the rest.

BACKGROUND OF THE INVENTION

Processes of the afore-described kind and also the corresponding teststands are sufficiently well known. Particularly well known areprocesses and devices for testing driving axles for trucks, to which thepresent invention is primarily to be applied. However, the features ofthe process and the device can also be applied without any further adoto other driving axles, wherein for instance only one single axle shaftis provided, which optionally can be directly driven or whose axletransmission does not have a differential.

The known processes and devices for the testing of driving axles havethe disadvantage that the testing is done under conditions which do notmatch the conditions under which the vehicle will later operate at allor are only able to match them to a limited extent. So, for instance,the axle housing is securely mounted in a frame, while the driven sidesof the axle shafts are connected in a wheel mounting with a rotatablepart, which is either directly braked or in turn drives a generator,which this way converts the energy transmitted by the axle shaft intoelectric current and also exerts a braking effect on the shaft, so thatthe entire axle is loaded with respect to its main function, namely theshifting and transmission of torque.

But later, during its operation, for instance of a driving axle mountedin a truck, conditions arise which cannot be duplicated with the stateof the art testing processes and the state of the art testing devices.Instead, in addition to the described purely functional test, furthertesting of the axle with other test stands and other test methods has tobe done, wherein the axle is loaded statically and dynamically, butwherein it can not be rotationally driven. As a result, several testshave to be performed on the axle in succession and these tests actuallyfurnish results of little value.

Finally, further complicated testing has to be done under trafficconditions, i.e. with a driving axle mounted in a vehicle or anotherdevice, which are correspondingly time-consuming and costly.

OBJECT OF THE INVENTION

It is the object of the present invention to provide an imporved testingprocess, as well as a testing device which will make it possible to testdriving axles under conditions coming as close as possible to actualoperational and traffic conditions.

SUMMARY OF THE INVENTION

This object is attained, in accordance with the invention in a processwherein during the testing of the total function of the axle, consistingof driving and carrying functions, the axle is placed under load byadditional forces, which do not depend on the drive and the brake.

Thus, while with the state of art process a driving axle was testedexclusively separate with respect to its driving function (shifting,conversion and transmission of torque), and independently therefrom withrespect to its carrying function (load), in accordance with theinvention, these two testing processes are performed in one singletesting process. The advantage of the process according to the inventionlies not only in the gain in time and assembly work, but also and mainlyin the fact that the testing conditions for the driving axle are muchmore realistic, since all concerned loads or additional forces actingupon the axle, have also an influence on the driving axle as atorque-transmitting unit.

The creation of such realistic operation conditions was up to nowpossible only when using the driving axle in traffic conditions, when acorresponding driving axle was mounted in a truck and this truck thenwould perform test drives. Of course such a procedure is extraordinarilycumbersome and, in addition, the survey of the functions and the controlof the load forces to which the driving axle is subjected can beperformed only with difficulty with such a process.

The process according to the invention combines on the one hand theadvantages of a testing under realistic conditions (as for instance intest drives) with the advantages of the testing on a test stand, which,corresponding to the desired data, is equipped with reading andmeasuring instruments.

The load produced by the additional forces mentioned above can consistof a predeterminable static basic load and an additional load,selectable according to size and frequency.

From the point of view of a pure axle load, conditions similar to thoseof a loaded truck traveling over uneven ground can be simulated.

Static based load and time-variable additional load are considered notonly with respect to vertically acting axle loads, but also with respectto propulsion, braking and acceleration forces or to flexural torque asit occurs at curves or in the case of sideward inclinations.

The advantages of the present invention will be most apparent fromexamples in the field of motor vehicles or trucks. It is, however,self-understood that the features of the invention can be applied withthe corresponding advantages also to other driving axles, such as boatdrives or, generally, machine drives.

According to the invention, it is provided that the additional forcesinclude propulsive forces. Such forces occur during braking andacceleration of motor vehicles and can amount to a value comparable tothat of the weight of a vehicle, whereby the resulting force is asummation of the weight force and the propulsive force, through vectoraladdition of the weight force and the propulsive force and has to beabsorbed by the bearings between the axle shaft and the axle housing.

Also in accordance with the invention, it is provided that theadditional forces include flexural torque.

As already mentioned, such flexural torque occurs when passing throughcurves or when a vehicle is in a sidewardly inclined position, since alaterally acting mass or inertial force, which theoretically acts of thegravity center of the vehicle, can be compensated by a frictional forcein the tire contact area, so that alltogether a torque acting on thevehicle, with reference to the tire contact area results, whereby theaxles or the axle shafts are under the stress of flexural torque.

The afore-mentioned additional forces complete the system of forces towhich the axle can be subjected, so that generally, during testing,realistic operational conditions can be simulated.

In the preferred embodiment of the invention it is provided that thedriving axle is integrated into a closed transmission circuit and is setunder load. In this connection, the gear loading refers to thetransmission circuit, which is set under load in such manner thatvarious operational conditions can be simulated, depending on the degreeof loading, conditions such as they occur during acceleration or up-hilldriving under heavy load. The closed-circuit transmission has therebythe advantage that the total energy to be used for driving a test axlehas to be equal to the energy converted into frictional heat in theentire transmission circuit. Additional energy, in order to produce onthe driven side frictional heat in a brake, or joule heat and additionalcurrent in a generator is not required, since the driving- and thedriven side are intercoupled, and any energy surplus on the driven sidecan be made available at the driving side. Thus, the process also workswith a lower specific energy consumption.

Finally, the process according to the invention, provides that theclosed-circuit transmission contain at least two objects to be tested ina row.

Since it is anyway necessary to have additional transmission elements inorder to close the transmission circuit, this can be done cleverlythrough a second object to be tested, i.e. a second driving axle. Thisoffers not only the advantage of simultaneous testing of two drivingaxles, but also the possibility to establish the product accuracy causedby finishing tolerances.

The device for testing driving axles for trucks, comprises a drivingunit generally linked by a driving shaft to the axle transmission,consisting of an axle housing with linking elements between the axleshafts and a braking unit producing the resistance to rotation.According to the invention, at the frame rigidly connected to the baseor mounting plate, force-transmitting elements are provided, which onone side are connected to the axle housing and the axle shaft and on theother side, with the frame or the mounting plate.

In this connection, it is self-understood that the force-transmittingelements do not only a holding function, but transmit preselectable andwell defined forces or make possible the measurement of the forcesacting thereon or transmitted by them. These force-transmitting elementscan on the one hand engage at the axle housing, as well as the axleshaft, while the reference point is formed by the frame, the foundation,or the parts which are rigidly connected thereto.

As a rule, such a device makes possible not only the testing of the axlefunctioning purely as a torque transmission system, but also the way itfunctions under additional loads.

In order to insure the axle loading, in accordance with the invention,it has been found to be advantageous to provide a crossbar over the axleand to connect this bar with the axle housing via spring elements.

With the aid of such a crossbar, the axle housing can be subjected toaxle loads in vertical direction, which then also act upon the axleshaft through the axle bearings. Since, in reality, axle loads areusually supported by spring suspension, here also suitable springsuspension elements are provided as force-transmitting elements. Thesecan also at the same time serve for measuring the transmitted forces.

Advantageously, the invention provides further that the axle housing beat least limitedly rotatable around the axle shaft with respect to theframe and connected to a force absorber running essentially tangentialto the theoretical wheel, through a lever of a length basicallyequivalent to half of the wheel diameter.

Such a force absorber measures directly the propulsive force driving thevehicle and which, according to the Newtonian principle ofaction=reaction, acts also on the corresponding axle bearings. Thisforce is produced by the reaction torque acting upon the axle housing,rotatable at least to a certain limit, when a resistance to rotation isopposed to the driving axle.

The preferred embodiment of the invention has, on the driven side, theaxle shaft rotationally driving a clutch housing, wherein a bending arm,rigidly connected to the axle shaft and constituting an extensionthereof, is movable vertically with respect to the rotation axis of thedriving axle, thereby producing flexural torque.

Such a bending arm can transmit flexural torque to the axle shaft, ofthe kind that occurs when driving through a curve or in a sidewardlyinclined vehicle. The axle is supported in at least one axle bearingclose to its driven end and is connected on the driving side with anaxle differential. Advantageously, the clutch housing contains aspherical toothed bearing for the part engaging with the axle shaft,permitting a tilting of this part with respect to the rotation axis.Because of this arrangement, it is possible to transmit the torquewithout any problems from the shaft to the clutch housing and thereby,in given cases, to all the transmission parts connected therewith, inspite of the flexural torque acting upon the axle shaft and theresulting bending.

It has been proven advantageous and suitable that the axle transmissionaccording to the invention be coupled in series with furthertransmission elements and at least one loading motor, into aclosed-circuit transmission.

As already mentioned, for testing a driving axle in a closedtransmission circuit it is necessary to have a driving power sufficientto overcome the total frictional energy produced in a closed-circuittransmission. The loading motor serves for the loading of the individualtransmission elements, so that they mesh with the correspondingfriction.

A preferred embodiment of the invention is one wherein a loading motoris provided, which in the case of a driving axle having a left and aright axle shaft, is connected on one side with the driven side of oneof the axle shafts (the left or the right one) via an intermediate shaftbridging the differential, and on the other side with the driven side ofthe other (the right or the left) axle shaft.

With the aid of a loading motor arranged as above it is possible to letone of the axle shafts run quicker than the other one. This of course isbased on the presumption that a differential gear is provided in theaxle, whereby the primary rotational speed is determined by an auxiliarydrive of the intermediate shaft. The differential speed of the two axleshafts corresponds to the simulation of driving through a curve.Thereby, additional flexural torque can be transmitted via theaforementioned bending arm to the axle shaft.

A particularly advantageous embodiment of the invention has two drivingaxles of the same kind with two axle shafts each coupled on the drivenside over two steering gear units and wherein one of the driving axlesis directly linked to the driving unit and the other driving axles islinked therewith in an indirect driving connection, via a loading motor.

Such a loading motor incorporated in the transmission circuit, caneasily produce a bracing between the two axle shafts, so that due tothis bracing the axles are driven under similar intrinsic load as theone produced by applying a brake or a generator at the driven end of theaxle shafts. However, thereby no surplus of energy should be produced bythe driving unit, which subsequently is to be converted in the brakingor generator unit into heating energy or partially also into electricenergy. The entire testing stand becomes more compact and cost-efficientas a result.

Finally, in the preferred embodiment of the invention it is providedthat driving axles of the same kind and an intermediate shaft equippedwith a loading motor be arranged in an L-shape, in such a manner thattheir rotation axes run basically parallel and that the rotation axes ofthe two driving axles form the terminal points of the L flanks while therotation axis of the intermediate shaft forms the point where the twoL-flanks meets. Because of this arrangement of the driving axles and theintermediate axle, both driving axles are advantageously accessible fromabove and can be set under load with the crossbar. In this way it ispossible to test simultaneously two driving axles.

BRIEF DESCRIPTION OF THE DRAWING

Further advantages, features and application possibilities of thepresent invention will become clear with the aid of the followingdescription of a preferred embodiment of the device and the accompanyingdrawing, through which the process is also explained. In the drawing:

FIG. 1 is a general perspective view of a testing stand with two drivingaxles;

FIG. 2a is a schematic cross section of an axle in the area of thetorque stay rod;

FIG. 2b is a schematic frontal view of a left axle half;

FIG. 2c is a top view of the apparatus shown in FIG. 2b; and

FIG. 3 is a diagrammatic cross sectional view of clutch housing forreceiving the driven end of an axle.

SPECIFIC DESCRIPTION

The entire transmission testing stand is built on a foundation formed bymounting plates 1, 1'. As shown in FIG. 1, on the mounting plate 1L-shaped frame parts 2, 2' are securely bolted in T-shpaed grooves 3 ofthe mounting plate 1. The frame segments 2, 2' can slide along thegrooves 3, for mounting or dismounting the axles.

Each frame segment 2, 2' comprises a angled gear units 5, 5'. Thereceiving spaces for the driving axles 4, 4' in the frame segments 2, 2'or the angled gear units 5, 5' are located in the flanks of the L-shapedframe segments. In the corner area of the frame segments 2, 2', wherethe two L-flanks meet, an intermediate shaft 6 is arranged, which isdirectly coupled with the angled gear unit 5' and is in drivingconnection with the angled gear unit 5 via the loading motor 7. Byactuating the loading motor 7, the angled gear unit 5 can either lead ortrail with respect to the angled gear unit 5', depending on thedirection of rotation of the loading motor 7. For the driving axles 4,4', which with their two driving ends are each in a rigid rotationalconnection with one of the two angled gear units 5, 5', this isequivalent to the simulation of going through a curve, whereby thedifferential contained in the axle transmissions 8, 8' balances thedifference between the rotation of the left axle shaft with the respectto the right axle shaft 9. The axle shaft 9 is surrounded by the axlehousing 10,10' in FIG. 1, while in FIG. 2c it is visible.

The drive unit 11 for the two driving axles 4, 4' consists of a drivingmotor 12, the return gear 14 arranged in the housing 13 and the loadingmotor 16. The loading motor has the effect that during driving, betweenthe two driven shafts 15, 15'--from now on referred to only as thecardanic shafts--a rotation is created, which is however limited to theresilience available within the system--consisting of cardanic shafts15, 15', driving axles 4, 4', steering gears 5, 5' and return gear 14.Thereby, the torque-transmitting components under load work against eachother, corresponding to the degree of the load imparted by the loadingmotor 16. In this way, a realistic testing of the function is possibleover the entire area under load. It is self-understood that the angledgear units 5, 5' and the return gear 14 are arranged in such a mannerthat it is possible to let the driving axles 4, 4' idle, without theactuation of the loading motors 7, 16.

The transmission circuit is built the following way: The driving motor12 drives the cardanic shaft 15 via the return gear 14, which shaftdrives in turn the axle shaft 9 of the driving axle 4, via the axletransmission 8 in the axle housing 10. The axle shafts 9, 9' of theaxles 4, 4' are connected over clutch housings 17 with the angled gearunits 5, 5'. Via the angled gear units 5, 5', the torque of the axleshafts 9 of the driving axle 4 is transmitted to the axle shafts 9 ofthe driving axle 4' and reacts on the return gear 14, over the axletransmission 8' of the driving axle 4' via the cardanic shaft 15'. Dueto the redirecting in the steering gear units 5, 5' and in the returngear 14, both cardanic shafts 15, 15' and both driving axles 4, 4' andtheir axle shafts, have the same direction of rotation.

In the above-described transmission circuit, through correspondingactuation of the loading motor 16, the driving axles 4, 4' can be in thedriving mode (positive torque load) or in the braking mode (negativetorque load). This simulation corresponds in the driving mode (positivetorque load) to acceleration processes, normal driving conditions and toup-hill driving with corresponding load assignment.

In the case of braking mode (negative torque load), the conditionscorrespond to the operational conditions during braking, also by meansof motor brake, skidding (e.g. during downhill driving) and reversedriving.

The special advantage of the present test stand and of the testingprocess performed therewith consists thus in the fact that not only apure functional testing of the driving unit with respect to thetransmission of torque from the driven shaft to the driving wheel takesplace, but that an additional loading of the driving axles 4, 4' can beachieved, which corresponds to the actual load to which the drivingaxles will be subjected when operating in a truck. Over the axle 4, acrossbar 18 can be discerned, which is supported via pneumaticshock-absorbers 19 on the axle housing 10. The crossbar 18 ishydraulically loaded from above, whereby also short-term loadalternations are possible. The crossbar 18 does not rest on the framesegments 2, 2', but is carried exclusively by the axle housing 10 or thedriving axle 4, via pneumatic shock-absorbers 19.

Further, underneath the pneumatic spring 19, torque stay rods 20, 20'can be seen, and their purpose will be explained later. These are bettershown in detail in FIG. 2a, which represents a cross-section through thedriving axle 4 along the torque stay rod 20. in FIG. 2a, the axle shaft9 can be discerned, which runs in axle bearings (not shown in thiscross-section) in the axle housing 10. In turn, the axle housing 10rests upon the axle shafts 9, 9', via axle bearings which among othersare located in the area of the wheel mounting 22, 22' (FIG. 1), the axlehousing being otherwise freely rotatable. When a torque is transmittedvia the cardanic shaft 15, the axle transmission 8 and the axle shaft 9,against a corresponding resistance, to the driven end of the axle shaft9-- which corresponds to starting, accelerating or also to maintaining acertain speed by overcoming air- and rolling-friction forces--thistorque transmitted on the driven side causes a countertorque actingfirst on the over the axle bearings and the axle transmission 8 on theaxle housing 10, attempting to rotate the latter in the oppositedirection. Since the axle housing 10 is connected to the vehicle framegenerally through (not represented) plate springs or other force- andtorque-transmitting elements, this torque is absorbed by the entirevehicle. This torque is also expressed during high acceleration by thedipping of the vehicle tail respectively the rising of its frontportion.

In the state of the art testing stands, the axle housing is rigidlymounted in the test stand and the torque is absorbed by the frame of thetest stand or the like. In the present test stand, the already mentionedtorque stay rods 20, 20' are provided for the absorption of the torque.Each torque stay rod 20, 20' is connected via a respective lever 23 (inthe schematic representation of FIG. 2a, only the lever 23 for thetorque stay rod 20 is shown), to the assigned force transmission element24. 24', which can be connected to the frame segments 2, 2'.

The effective length of the lever 23 (marked with "x") i.e. the distancebetween the rotation axis 25 and the application point of the forcetransmission element 24, corresponds exactly to the distance of thewheel contact area 27 of a driving wheel 21 provided for the drivingaxle. The driving wheel 21 is shown in broken lines for a betterunderstanding. The actual presence of a driving wheel is otherwise notrequired in a test stand and also not provided.

Since the reaction torque, i.e. the torque acting on the axle housing 10(arrow 46) is equal to the driving torque (arrow 45) based on theNewtonian principle action=reaction, the force (arrow 31) measured inthe force transmission element 24 corresponds also to the propulsiveforce acting upon the vehicle, respectively upon the axle bearings (notrepresented here). Together with the loading of the axle housing 10,respectively the axle bearings, via the crossbar 18 and the pneumaticshock absorbers 19, 19', the axle bearings of the axle 4, 4' (due to theincorporation of a further crossbar) are additionally loaded with thepropulsive forces produced during driving, which are measurable with theaid of the force transmission elements 24, 24'.

In the schematic illustration of FIGS. 2b and 2c, the arrangement of thetorque stay rod 20 with respect to the axles 4, 4', respectively theirdifferential gearing 28 and the contact level 43 of the wheel 21. Thereaction force to the torque appears--such as shown by arrow 31--in thetorque stay rod level 44. Due to the distance "y" between the wheelcontact level 43 and the torque stay rod level 44, a loading torquesimilar to the one existent during vehicle operation, acts upon the axleshaft 9 or axles 4, 4'.

FIG. 3 shows the already mentioned clutch housing 17, through which theaxle shaft 9 is connected to the angled gear unit 5 or 5' (FIG. 1). Theaxle shaft 9 is connected rigidly, via wheel mounting 22, 22', to awheel center disk 33 which corresponds to the wheel center disk of avehicle. However, in this case the wheel center disk 33 differs anactual wheel disk from, since it has a spherically shaped toothing 34,which, together with a correspondingly shaped toothing in the bearinghousing 35, forms a spherical toothed bearing 36. The spherical designof the toothed bearing 36 makes possible the tilting of the wheel centerdisk 33 with respect to the rotation axis 25. When going through a curveor when the vehicle is in an inclined position on a grade, due to thevehicle mass, forces are produced which act upon the wheel center disk33 via the lever arm formed by the wheel contact area 27 (FIG. 2a) andthe rotation axis 25, thus inducing a moment in the wheel center disk33. In this way, the axle shaft 9 is correspondingly set under load.Such flexural torque acting upon a wheel center disk can also besimulated realistically, with the aid of the clutch housing 17, assistedby the bending arm 37. For this purpose, the external end of the bendingarm 37 is provided with a spherical head 38, as shown in FIG. 3, whichis correspondingly supported at 39 and is also designed as a sphericalbearing. The desired, respectively required flexural torque acting onthe axle shaft 9 is produced by the hydraulic cylinder 40, which islinked to this bearing.

The shaft 9 thereby drives the bearing housing 35, via wheel center disk33 and its toothing 34, the bearing housing being supported in thebearing 41 and standing in a form-locking rotational connection with theremaining parts of the angled gear units 5, 5', via gear 42.

The loading motor 7 is connected with one of its driving elements to theangled gear unit 5, while the other driving element of the loading motor7 is connected to the opposite angled gear unit 5' via intermediateshaft 6. When the loading motor is actuated, it produces a relativerotation between its driving elements, so that the angled gear units 5,5' are no longer synchronized, but one rotates quicker than the other.As a result, the driving shafts 9 on the one side of the driving axles4, 4' rotate more rapidly than on the other side. These rotationalmovements with a different speed are made possible by the differentialin the axle transmissions 8, 8'. Such an operation corresponds to goingthrough a curve, whereby the operational rotational speed of theintermediate shaft 6 is imparted by an auxiliary drive (not shown).

The loading motor 7 is a hydraulic loading motor with infinite angle ofrotation, i.e. it is possible to simulate curve rides of desired length,or also wheel failure. In opposition thereto, the loading motor 16 needsonly a very small angle of rotation, but it can also be a hydraulicloading motor with infinite angle of rotation, like the loading motor 7.

In conclusion, with the presently described test stand and thecorresponding process, two driving axles can be simultaneously tested,whereby all the static and dynamic loads, to which the axle is subjectedduring operation, can be realistically simulated, and, at the same timethese loads can be precisely measured, in order to make possible tojudge the finishing inaccuracies in the evaluation measurement data. Theconcept of finishing inaccuracies encompasses in the largest sense allsources of failure, which can result from for instance tolerances,material failure, and so on and can show up in the various components.

I claim:
 1. A method of testing driving axles for motor vehicles,comprising the steps of:mounting at least one driving axles inrespective gear units at opposite ends in a test stand so that said axlehas opposite axle shaft ends at said gear units and an axle housingextending between said units and supported on said stand; connecting adrive motor to one of said ends through one of said units and a load tothe other of said ends through another of said units for driving saidaxle while loading same; and applying to said axle on said test stand aplurality of other forces independent of forces applied by said drivemotor and load and sufficient to enable testing of total function of theaxle under simultaneous drive and carrying conditions, the applicationof said other forces including application to said shaft ends of dynamiclateral forces corresponding to wheel-disk reaction forces applicable tothe axle in use.
 2. The method defined in claim 1 wherein saidapplication of other forces includes application to said axle of apredetermined static force and, in addition to said predetermined staticforce an additional load selectable as to magnitude and frequency. 3.The method defined in claim 2 wherein said application of other forcesincludes application to said axle of propulsive forces.
 4. The methoddefined in claim 3 wherein said application of other forces includesapplication to said axle of flexural torque.
 5. A method of testingdriving axles for motor vehicles, comprising the steps of:mounting atleast one driving axles in respective gear units at opposite ends in atest stand so that said axle has opposite axle shaft ends at said gearunits and an axle housing extending between said units and supported onsaid stand; connecting a drive motor to one of said ends through one ofsaid units and a load to the other of said ends through another of saidunits for driving said axle while loading same, and mechanicallycoupling said drive motor to said load to form with said axle a closedtransmission circuit loading said axle by tensioning across saidopposite ends; and applying to said axle on said test stand a pluralityof other forces indpendent of forces applied by said drive motor andload and sufficient to enable testing of total function of the axleunder simultaneous drive and carrying conditions.
 6. The method definedin claim 5 wherein at least two axles to be tested are mounted in saidtransmission circuit in a row.
 7. The method defined in claim 6 whereinthe application of said other forces includes application to said shaftends of dynamic lateral forces corresponding to wheel-disk reactionforces applicable to the axles in use.
 8. The method defined in claim 8wherein said application of other forces includes application to saidaxles of a predetermined static force and, in addition to saidpredetermined statis force an additional load selectable as to magnitudeand frequency.
 9. The method defined in claim 8 wherein said applicationof other forces includes application to said axles of propulsive forces.10. The method defined in claim 9 wherein said application of otherforces includes application to said axle of flexural torque.
 11. Anapparatus for testing driving axles for motor vehicles, comprising:atest stand having a base and a pair of gear units spaced apart on saidbase; means for mounting at least one driving axle in said gear units atopposite ends so that said axle has opposite axle shaft ends at saidgear units and an axle housing extending between said units; a drivemotor connected to one of said gear units and to one of said endsthrough said one of said units and means for connecting a load to theother of said ends through another of said units for driving said axlewhile loading same; and means on said stand engageable with said housingand with said shaft ends for applying to said axle on said test stand aplurality of other forces independent of forces applied by said drivemotor and load and sufficient to enable testing of total function of theaxle under simultaneous drive and carrying conditions, said means forapplying said other forces including means for application to said shaftends of dynamic lateral forces corresponding to wheel-disk reactionforces applicable to the axle in use.
 12. The apparatus defined in claim11 wherein said means for applying said other forces includes a crossbardisposed above said axle housing, and spring elements connecting saidaxle housing to said crossbar.
 13. The apparatus defined in claim 11wherein said means for applying said other forces includes a leverhaving a length of half a diameter of said wheel connected to saidhousing, and a force transmission element oriented generally in atangential direction with respect to the orientation of said wheelconnected to said lever and displacing same to apply torque to saidhousing.
 14. The apparatus defined in claim 11 wherein said means forapplying said other forces includes a clutch housing connected to saidaxle at said other of said ends and enclosing a bending arm rigidlyconnected to said other of said ends and displaceable perpendicularly toa rotation axis of said axle shaft ends.
 15. The apparatus defined inclaim 14 wherein said clutch housing contains a spherical toothedbearing for a wheel-center disk and means enabling tilting of said disk.16. The apparatus defined in claim 11 wherein said load includestransmission elements connected to said motor whereby said motor, saidaxle and said transmission elements form a closed transmission circuit.17. The apparatus defined in claim 11 wherein said load includes meansfor connecting a second driving axle in series with the first mentioneddriving axle.
 18. The apparatus defined in claim 17 wherein said meansincludes an intermediate shaft between said gear units parallel to saidaxis and said load further includes a load motor operatively connectedto said intermediate shaft.